Well, the original novel had Violette going mad, bullying her half-sister and even attempting to kill her while basically being a stalker to Claudia, it was absolutely darker.
Heck, she says that no one went to visit her in prison while she basically made it so she died of hunger, so i assume Yulan got tired of being ignored, had found someone else or didn't want to date a bullying wannabe murderer, honestly, the new timeline is much better for everyone involved.